1. Field of the Invention
This invention relates to a process for producing exopolysaccharide from submerged mycelial culture of mushroom and more particularly, to the process for improving the exopolysaccharide production from the mycelia using the different bistage pH control technique comprising the steps of; (1) a process for the production of mycelia whose pH conditions in a batch medium are kept constant at 2 to 6 at the initial pH, while adding ammonium ion to the medium, and (2) a process for the production of exopolysaccharides whose pH conditions in a batch medium containing the mycelia are adjusted to 3 to 7.
2. Description of the Related Art
Mushrooms have attracted a great deal of interest in many areas of foods and herbal drugs, etc. The main components used for biological applications are polysaccharides, which exists within the mushrooms or in its secretion. Recently, the study of exopolysaccharides (EPS) has been conducted extensively, since their production processes from culture broth do not require extra steps and they require relatively simple purification processes. However, it has been very difficult to culture large amounts of mycelium in a large-scale fermentor in order to produce reasonable amounts of EPS. There have been several limitations in scaling-up the mycelial culture system due to its low secretion level and changes in the physical properties of the culture broth such as viscosity, morphology, etc. A major problem in cultivating the mycelium is the increase of viscosity of culture broth when the mycelium grows, which results not only in limiting oxygen transfer, but also in building up shear stress. High shear stress has a negative effect on the morphology of the mycelium which can directly reduce the cell growth along with EPS production. No attempts have been made to show the effect of adding ammonium ion in previous work, even though the mycelial cells were grown in ammonium ion containing medium. For filamentous fungi, it is well known phenomenon that cell growth was increased by adding ammonium ions, possibly due to their role of facilitating carbon accumulations. However, a repressive effect of excessive ammonium ions on antibiotic production has also been reported.
Meanwhile, Ganoderma lucidum belongs to family Polyporaceae and its fruiting bodies are called Ganoderma lucidum. Hitherto, it has been proved to have various therapeutic efficacies such as antihypertension, diuresis, cardiac stimulation, cardiotonic, etc. In an effort to produce Ganoderma lucidum, the solid cultivation method using saw or lumber has been mainly applied in a farmhouse, but the conventional method has some drawbacks because a longer cultivation time is required with intensive labor and the extraction process of polysaccharides from the fruiting bodies has met with difficulty.
To comply with this matter, a batch cultivation method has been widely used with the following advantages: (1) cultivation can be made available under constant conditions at all times, (2) the mycelium of homogeneous quality can be obtained in high yield and with large-scale production, and (3) the production cost is reasonable. However, the batch cultivation method for industrial use has recognized some disadvantages in that its extraction process for polysaccharides (xcex2-1,3-glucan of antitumor activity), active ingredient of Ganoderma lucidum, from the mycelium is very complicated and its yield is quite low.
Further, unlike the intensive studies for lower bacteria, the morphological and rheological studies for higher bacteria such as Ganoderma lucidum belonging to family Polyporaceae have yet to be elucidated during the batch cultivation, and the correlation between Polyporaceae and EPS production has not been reported. More specifically, it is important to make intensive studies on the correlation for a large-scale EPS production. In particular, to ensure the stability and productivity of the EPS, the changes in morphological and rheological parameters should be connected to mycelial concentration and their products, while cultivating the mycelium with different cultivation conditions. Currently, there is an urgent need for the research of various factors related to Ganoderma lucidum (e.g., pH, nitrogen source, mycelial morphology and rheological parameters, correlation between cell growth and EPS production).
To overcome the aforementioned shortcomings, the inventor et al. have conducted intensive studies that since the optimal conditions of both mycelial growth and EPS production are different each other, the EPS production is effectively improved in such a manner to optimize the cultivation conditions in the batch medium depending on each of desired products. Thus, this invention has been completed.
Therefore, an object of this invention is to provide a large-scale EPS production using the different bistage pH control technique from the mycelial production and EPS production.